Adaptation of ventilation to 'buffeting' in vehicles.

Objectives: Short exposures to buffeting in a vehicle driving over rough terrain induce an increase in the frequency of respiration resulting in hyperpnoea and hypocapnia. The present study investigates the adaptation to buffeting-induced hyperpnoea.

Methods: We monitored ventilation and cardiovascular function in nine healthy young adults prior to, throughout and post a 30 minute simulation of buffeting.

Results: All subjects had a consistent elevation of respiratory frequency throughout motion. End-tidal CO(2) decreased during the first 5 minutes of buffeting due to a transient increase in minute ventilation. Elevation of respiratory frequency was facilitated by shortening of inspiration without change in expiratory time. Tidal volume was maintained which resulted in an increase in mean inspiratory flow during buffeting. At later stages of motion there was a partial return to normal for mean inspiratory flow, minute ventilation and end-tidal CO(2)because of a slight reduction in tidal volume whilst inspiratory time remained shortened. Salivary cortisol levels were unaffected by motion, suggesting that the hyperpnoea was not secondary to non-specific stress.

Interpretation: The cause of elevated respiratory frequency during buffeting could be due to mechanical action on the torso, vestibular-respiratory drive or a protective reinforcement of the torso.